[pulseaudio-discuss] Virtual loopback to provide PCM capture

[Davide Cescato]

Thank you, Michał and Colin, for your precise answers! I have been 
looking for a solution for weeks, and you gave it within minutes of my 
request... Internal audio capture works perfectly.

Actually I now have a somewhat related question, for another unrelated 
task I have in mind: recording voip phone calls. What I currently can do 
is recording from the microphone input, which picks up both my voice and 
the other person's voice coming through the speakers. However, the path 
"out through the speakers and in through the microphone" adds a lot of 
noise to the other person's voice.

So, is it possible to somehow set up PA to let me capture a mixed stream 
containing both the internal audio stream carrying the other person's 
voice and the microphone input, so that both voices can be captured in 
good quality? Of course, I would wear headphones to hear the other 
person's voice and to block it from going through the speakers.

The problem with this approach is that the voip application should only 
capture the microphone input, whereas the recording application should 
capture the mix of both microphone input and "internal audio".

One (uneducated) guess of mine is that if there would be a monitor 
stream for the microphone input, I could mix it into the internal audio 
stream that I could then capture. I do not know if this is feasible, though.

Thanks!


On 06/29/2009 12:26 AM, Colin Guthrie wrote:
> 'Twas brillig, and Davide Cescato at 28/06/09 22:45 did gyre and gimble:
>> Hello,
>>
>> thanks for the work on PulseAudio! I would like to ask a question, and
>> will try to be as precise as I my limited knowledge allows.
>>
>> I would like to capture the audio on the PCM channel, i.e., the mixed
>> sound stream that is sent to my notebook's speakers. I have read in
>> forums that Windows Vista achieves the behaviour I am aiming at by
>> offering a virtual audio channel called "what you hear" among the list
>> of capture sources.
>
> Yeah pulse does this automatically. Every output device (or sink) has a
> "monitor" source.
>
> Sources are just pulses way of saying "input device", so recording from
> the mic or line in or a "monitor source" is exactly the same.
>
> So if your app is implementing direct pulse support, you can easily
> record from these montitor sources. You can see the sources in
> pavucontrol under the "Input Devices" tab provided you pick the right
> drop down.
>
> Col
>
>